Drilling muds



United States Patent 3,410,797 DRILLING MUDS Raymond W. Walker, Union,and Hugh E. Ramsden,

Scotch Plains, N..l., assignors to Esso Research and EngineeringCompany, a corporation of Delaware No Drawing. Filed Nov. 13, 1964, Ser.No. 411,115 4 Claims. (Cl. 252-85) ABSTRACT OF THE DESCLOSURE Certainorganotin dithiophosphate compounds, e.g. dibutyl tindidecyldithiophosphate and stannous bis (didecyldithiophosphate), inwater base drilling muds reduce the tendency of the drill pipe to becomestuck during drilling.

The present invention relates to improvements in the drilling of wellsand, in particular, to improved drilling fluids used in rotary type welldrilling processes. More particularly, the invention relates to drillingmuds having proper-ties which inhibit or prevent the sticking of drillpipe and drill collars.

In the drilling of wells by the rotary method, a drilling fluid iscirculated down the drill string and up the annulus between the drillstring and the borehole wall, while the drill string and drill bitattached thereto are rotated. Drilling muds used as the circulatingfluid are essentially suspension of solids in water; these solids formthe bulk of the mud filter cake. In general, the solids are clays andbarite and their relative amounts present in the bulk mud arecontrollable within limits set by the required mud density. Importantfunctions of drilling muds are: to clean the borehole of chips andcuttings and carry these to the surface; to lubricate the drill bit anddrill stem; to form a filter cake to seal and maintain the walls of theborehole and prevent formation damage; to control the pressure on theannulus to prevent blowouts or formation breakdowns and lost returns; tosustain the cuttings in the event of rig shutdown, so that these do notfall to the bottom of the hole and stick the drill pipe; and to protectthe surrounding formation in order that the wellbore may thereafter besuccessfully surveyed by known well-logging methods.

Sticking of drill pipe and drill collars during the drilling of wells isa well-known problem. When drill pipe and drill collars contact the Wallof the borehole, they become imbedded in the fiter cake and a force iscreated which pushes the pipe and collars against the borehole wall.This force is equal to the product of the area per unit of length of thepipe imbedded in the filter cake, the length of the pipe imbedded, thedifference between the hydrostatic drilling fluid column weight and theformation fluid pressure, and the coeflicient of friction between thepipe and filter cake. This type sticking is commonly referred to asdifferential pressure sticking or wall sticking. Another force whichcauses sticking occurs from purely mechanical causes. For example, anabrupt change in direction of the borehole may cause bending of thedrill pipe and the resistance to this bending may give rise to asufficiently large force holding the pipe against the borehole wall tocause sticking. Thus, the drill pipe is forced against the borehole wallin some manner and the resistance to movement of the pipe against themud cake is greater than the pulling forces available, which results inthe pipe becoming stuck in the borehole and necessitates an expensivefishing job.

To inhibit or prevent sticking of drill pipe and drill collars, manyexpedients have been tried. It is common practice to spot oil in thewell over the section where the pipe is stuck and this practice oftenallows the pipe to become loosened. Another practice that reduces, butdoes not eliminate pipe sticking is to emulsify oil in the drilling mud.To enhance the effectiveness of the oil emulsion muds in this respect, anumber of special oils have been tried that are alleged to be betterthan the commonly used diesel oil or kerosene. Unfortunately, themajority of these special oils, other than certain kerosenes havingnonfluorescent properties, introduce into the circulating mud system afluorescent material that interferes with the eologic evaluation of theformation core and cuttings samples by confusing the oil naturally inthe sands with the oil of the circulating mud, and for this reason,their use is drastically restricted.

According to the present invention, it has been found that certainorganotin compounds are very effective drillmg mud additives. Theorganotin compounds to which the present invention is directed may bemore accurately defined by the following general formula:

wherein 3 :0 to 3, 1:1 to 3, and y+z= an even integer from 2 to 4. R isan organo radical containing 2 to 18 carbon atoms and selected from thegroup consisting of alkyl, alkenyl and aralkyl. R is an organo radicalcontaining 2 to 18 carbon atoms and selected from the group consistingof alkyl, alkenyl and aralkyl. R is an organo radical containing 2 to 18carbon atoms and selected from the group consisting of alkyl, alkenyland aralkyl.

Examples of suitable compounds include but are not limited to stannousbis(didecyldithiophosphate), dibutyl tin bis didecyldithiophosphate,didecyltin bis diisobutyldithiophosphate, dibenzyltin bisdioetyldithiophosphate, diethyltin didodecyldithiophosphate, butyltintris dedicyldithiophosphate, tripropyltin dibenzyldithiophosphate. Apgeferred compound is dibutyltin bis didecyldithiophosp ate.

Preparation of the compounds having the above formula may be eflected byany of the methods known to the art. For example, in one such method anorganotin halide represented by the following formula:

wherein y, z, y-l-z, and R are as above defined and X is a reactivehalogen, such as chloride, bromine and iodine,

is reacted with a salt of dithiophosphoric acid represented by thefollowing formula:

wherein R and R" are as above defined and M is a cation, preferably ametal equivalent of hydrogen. Alkali and alkaline earth metals, such assodium, calcium, and the like, may be used. Ammonium or amine salts mayalso be used. The dithiophosphates are prepared by wellknown methods.

The additives ofthe present invention may also be prepared by reactingan organotin oxide represented by the following formula:

wherein R is as above defined, with a dithiophosphoric acid representedby the following formula:

s on

HS I

wherein R' and R" are as above defined.

W-hile various methods of preparing the additives of the presentinvention have been briefly mentioned, still other methods will beapparent to those skilled in the art and it is intended that alladditives having the general formula described above be includedregardless of their method of preparation.

The additives of the present invention are added to drilling mud inproportions of about 0.001 to 1.0% by weight, preferably about 0.01 to0.1% by weight. A most preferred drilling mud contains about 0.05% byweight of the additive of the present invention.

This invention is applicable to all of the clay-type drilling mudsnormally employed in rotary drilling. Such muds may simply compromisesuitable clays dispersed in water or they may contain other addedmaterials such as quebracho, lignin sulfonates and the like. Clay-ladendrilling fluids of densities and viscosities that are suitable forrotary drilling generally range in density from about 9 to about 11.5pounds per gallon. If heavier drilling fluids are needd, finely groundheavy minerals, such as barite, hematite, pyrite or siderite may beadded since these materials will contribute high density without undulyincreasing the viscosity of the drilling mud.

To evaluate the effectiveness of drilling mud additives in decreasingthe tendency for drill pipe to stick, a wellknown Stickometer Test wasused to measure the sticking coefficient which is defined for purposesherein as the ratio of the pulling force to the perpendicular force atthe time of the measurement. Essentially, the sticking coeflicient is ameasure of how strongly pipe becomes stuck in the presence of a givenmud system after a certain residence time under a specifiedperpendicular force.

The sticking coeflicient is defined for purposes herein as thetangential force required to move a plate over the mud filter cakedivided by the force normal to the plate. This may be expressed as:

Thus, the sticking coefficient is a dimensionless quantity correspondingto a coefficient of friction; however, unlike coefiicient of friction itis not a constant, but is time dependent and dependent on the thicknessand composition of the filter cake as well. However, by testing atconstant filter cake thickness and time, the composition remains as themajor variable. Differences between the sticking coeflicents of the mudwith and without additive are expressed as percent sticking tendency.

In order to demonstrate the utility and efficacy of the presentinvention, the sticking coeflicient was experimentally determined fordrilling muds of various compositions, using the followin technique:

The stickometer consists of a stainless steel cylindrical pressurevessel about 3" in diameter and 4" high. This vessel has a centrallylocated drain hole in the bottom. A core sand filter (porous sandstone)about 2" in diameter and 1" thick is positioned centrally in thepressure chamber over the drain hole. A stainless steel torque plate,which is about 2" in diameter and /8" thick and equipped with a diameterstem about 3" in length, graduated in intervals, is positioned on top ofthe core sand filter. The mud slurry (sample) is poured in the vessel towithin of the top. The cover is placed on the vessel, with the graduatedstem extending through the top and the cover is tightened. Five hundredpsi nitrogen pressure is maintained on the mud sample. The depth of thetorque plate is recorded and the plate is immediately released from thecore filter surface. The pressure keeps the plate at its top position.The pressure forces water out of the slurry and builds up a mud depositon the core filter. After the mud cake has built to thickness, thetorque plate is held against the mud cake until it sticks to it. Thefirst torque reading is taken five minutes after the torque plate hasstuck to the mud cake. Readings are taken at these intervals:5-10-15-20-30-45 and each succeeding 15 minutes up to and including 2hours, the point at which comparisions of sticking tendency are made.Torque readings are then taken with a torque wrench which fits to thetop of the torque plate stem.

The sticking coefficient is calculated by the following:

Sticking coefiicient=torque reading 0.00095 The sticking coeflicient ofthe additive-containing mud is compared with the mud value withoutadditive and the percent reduction sticking tendency is obtained.

Tests conducted with various compositions showed that for best results adrilling mud containing an additive of an organotin compound of thepresent invention must be present.

A typical base mud is one composed of about 68.5 gm. bentonite clay(Aquagel), 100 ml. water, 11.5 gm. ferrochromlignosulfate (Q-Broxin),3.5 gm. sodium hydroxide, 1230 gm. barites (Baroid), and 146 ml.kerosene.

A drilling mud was prepared having the above-described typicalcomposition. The sticking tendency of this mud was measured using theabove-described Stickometer Test. Various compounds, including additivesof the present invention, were added to the base mud and the respectivesticking coefiicients were determined. The results of this series oftests are shown in Table I.

TABLE I Percent Sticking Reduction Coetliclent Sticking TendencyDrilling Mud-no additive. 0.065 Drilling Mud plus 0.5% dibutyl ddithiophosphate 0. 044 32-33 Drilling Mud plus 0.05% dibutyl tindidecyldithiophc sphate 0. 044 32-33 Drilling Mud plus 0.0 dibutyl tindidecyldithiophosphate 0. 050 21-22 Drilling Mud-no additive 0. 084Drilling Mud plus 0.02% dibutyl tin dialkyl dithiophosphate 0. 076 0-10Drilling Mud plus 0.1% stannous bis(didccyldithiophospliate) 0. 06427-28 Drilling Mudno additive. 0. 082 Drilling Mud plus 0.1% stannictetrakis (didecyldithiophosphate) 0.081 0 In the preparation of thiscompound the dialkyl dithiophosphoric acid was a mixture of C4 and Cdithiophosplioric acids.

Results in Table I show that of the various additives tested only theorganotin compounds of the present invention significantly reduce thesticking tendency of the base mud.

What is claimed is:

1. A water base drilling mud comprising water and clay to which has beenadded a small amount, sufficient to reduce the sticking of drill pipe ina bore hole during drilling when using said drilling mud, of an organotin compound selected from the group consisting of stannous bis (didecyldithiophosphate) and dibutyl tin didecyl dithiophosphate.

2. A drilling mud as defined by claim 1 wherein said compound is dibutyltin didecyldithiophosphate.

5 6 3. A drilling mud as defined by claim 1 wherein said 3,047,4947/1962 Browning 252-8.5 compound is stannousbis(didecyldithiophosphate). 3,219,580 11/1965 Stratton 2528.5

4. A drilling mud as defined by claim 1 wherein said small amount is inthe range of about 0.001 to 1.0 wt. OTHER REFERENCES Percent 5 Rosenberget 21]., Increased Drill Bit Life Through Use References Clted ofExtreme Pressure Lubricant Drilling Fluids, article UNITED STATESPATENTS in Journal of Petroleum Technology, vol. 11, August 2,364,28312/1949 Freuler 252 32.7 1959 195 to 2,786,812 3/1957 McDermott 2s2 32.72,959,544 11/1960 Smith et a1. 252-32.? 10 HERBERT GUYNN pr'mary Emmmer

